Sound Transmission Loss

The testing of sound transmission loss at National Acoustic Laboratories is the primary use of
the reverberation chambers. The test aperture between the chambers consists of a 10 m2 opening in
which the test specimen (or wall) is constructed. The wall may consist of masonry, lightweight with stud
framing or other innovative products.

The test procedure is carried out in accordance with AS 1191-2002 "Acoustics - Method of Laboratory
Measurement of Airborne Sound Insulation of Building Elements". The data obtained in this measurement
is then manipulated in accordance with AS/NZS 1276.1-1999 "Acoustics - Rating of Sound Insulation in
Buildings and of Building Elements Part 1: Airborne Sound Insulation".

There are two recognised methods of determining sound transmission loss, the first is the American Sound
Transmission Class (STC). The second is the International Weighted Sound Reduction Index (Rw).

As a guide, the sound transmission loss for some typical materials are listed below:

The STC is similar to the Rw. Recently the spectrum adaptation term (Ctr) has become
more important as the Building Code of Australia now require products to be rated to determine this value.
The Ctr is added to the Rw to obtain an overall Rw + Ctr value.
New apartment buildings are required to achieve Rw + Ctr 50 or better for common walls
and floors.

Sound transmission loss testing may be carried out over two hours for a single product, however several
hours or days may be required for the product to properly cure prior to testing. Laboratory hire rates
may be negotiated on a daily rate or for the total number of products to be tested.